﻿<p>An advanced face is a specialization of a face surface that has to meet requirements on using particular topological and geometric representation items for the definition of the faces, edges and vertices.</p>

<p>An <em>IfcAdvancedFace</em> is restricted to:</p>
<ul>
<li>have a face surface geometry of type <em>IfcElementarySurface</em>, <em>IfcSweptSurface</em> or <em>IfcBSplineSurface</em>,</li>
<li>have one <em>IfcFaceOuterBound</em> as the bound of the face, with the exception of closed surfaces,</li>
<li>have all faces to be bound by <em>IfcEdgeLoop</em> or <em>IfcVertexLoop</em>,</li>
<li>have all edges to have an edge curve geometry,</li> 
<li>have the edge curve geometry restricted to <em>IfcLine</em>, <em>IfcConic</em>, <em>IfcPolyline</em>, or <em>IfcBSplineCurve</em></li>
</ul>

<p>In case of closed faces with periodic surfaces, such as cylindrical or spherical surfaces, the following applies:</p>
<ul>
<li>the edges of the closed surface, in case of a cylindrical surface the upper and lower cap, refer to the same instance of <em>IfcVertexPoint</em> twice,</li>
<li>no <em>IfcFaceOuterBound</em> is provided, or the <em>IfcFaceOuterBound</em> is constructed using an <em>IfcSeamCurve</em> at the periodic end of the underlying closed surface, in case of a cylindrical surface at 0./360. degree.</li>
</ul>
<table summary="periodic closed surface">
 <tr>
  <td style="width: 600px"><img src="../../../figures/ifcadvancedface_01.png" alt="cylindrical surface"></td>
 </tr>
 <tr>
  <td><p class="figure">Figure 2 &mdash; Use of <em>IfcCylindricalSurface</em> as underlying surface of an <em>IfcAdvancedFace</em></p></td>
 </tr>
</table>
<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>advanced_face</strong> defined in ISO 10303-511.</blockquote>
<blockquote class="history">HISTORY&nbsp; New entity in IFC4</blockquote>